The research in this project is aimed at determining the mechanism by which rhodopsin excites the visual receptor. Characteristics of rhodopsin which reveal general properties of membrane structure and function are also being investigated. The techniques employed include flash photometry, microspectrophotometry, osmotic permeability studies, atomic absorbance observations of ion content, and indicator dye techniques for ionic activity measurements. Chromophore motions in bacteriorhodopsin and light-scattering changes in Halobacteria are also being studied.